Best Album Purchase, or Best Evaluating Record


I would just like to know what you consider your best album purchase ever, or your choice of album used to evaluate a stereo system.

My best purchase has to be about 300 - 400 classical records, for $300, that contained many mint shaded dogs, Living Presence, and blue Backs (among others).
licoricepizza
Whenever I do a tweak or an upgrade, I reach for the Diana Krall Christmas Songs LP, and not the 200g black version, but the 150g transparent red version. It sounds wonderful. It has everything--SOTA analog source recording, great mastering, female vocals, lush orchestrations, sleigh bells and assorted percussion.

I also have to give mention to "Class of '78," a direct-to-disc of the Buddy Rich Big Band. That's the record that launched my latter day vinyl craze. I took that LP and its companion SACD to my local high end store and had the sales guy spin them both through a pretty expensive all-Linn system. That was that and I haven't bought any digital music since, and I didn't even listen to any for over a year.
I really like the M&K Lp 'For Duke' as a reference recording..This LP really has some of the best sounds
recorded IMHO and shines on my system
I use quite a few LP's. A number of Bill Evans (Spring leaves, At Shelly's Mane Hole - I don't yet have a copy of Debbie) Oscar Peterson Night Child on Pablo is fantastic. Brubeck A La Mode and Time Out, Athena's Symphonic Dances, Sufjan Steven Illinoise, Nora Jones, Feels Like Home (CLassic Reissue) Fiona Apple's Extraordinary Machine (just the title cut), Rickie Lee Jones Pop Pop and her first title (most RLJ sounds very good) Joe Jackson Body and Soul, Satchmo St. James Infirmary, Brubeck Discovered Again (a little boring) Paul CHambers Bass on Top. Greateful Dead's Reconning - a great live acoustic set. I also use, and get ready for this, Springsteen's Devils and Dust. I never get tired of listening to the title cut, and Reno. I bought that Suziki String Band on Bkonig's recommendation. It's really nice sounding but I guess I don't like it musically. I'll have to give it another listen.

For digital playback, Patricia Barber's Companion is my reference. I'll have to get that one on LP, though I know it's a digital recording.